Media captionThere was heavy gunfire as armed men took the police station in Kramatorsk

Pro-Russia militants have taken over a police headquarters in the eastern Ukraine city of Kramatorsk, local media and witnesses say.

This followed a gun battle with the police defending the building as the attackers stormed it.

Several other official buildings were reported to have been seized in Donetsk region on Saturday.

The confrontations come amid rising tension between the new government and pro-Russia protesters.

Eastern Ukraine has a large Russian-speaking population and has seen a series of protests since the ousting of pro-Russian President Viktor Yanukovych in February.

The new government in Kiev accuses Moscow of orchestrating the unrest in eastern Ukraine. But Russia denies responsibility.

We are not Ukrainian troops, we are people's militia. We have risen up to drive away the corrupt Kiev policeGunmen in Kramatorsk

Amid mounting concern about the situation, US Secretary of State John Kerry called his Russian counterpart Sergei Lavrov.

Mr Lavrov said Ukraine was "demonstrating its inability to take responsibility for the fate of the country".

He warned that any use of force against Russian speakers in eastern Ukraine would undermine the "potential for co-operation", which included talks in Geneva next week.

It has also been announced that US Vice President Joe Biden is to travel to Ukraine in 10 days' time.

Flag raised

A Kramatorsk-based website said the attackers arrived in the city in two buses at around 1900 local (1600GMT) on Saturday and seized the police department after an exchange of fire lasting several minutes.

There had been no casualties and the flag of the Donetsk Republic had been raised at the building, the Voctochnyy Proyek site said.

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Protesters have held the administration building in the regional centre Donetsk since last Sunday

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A police station in Sloviansk was taken over on Saturday by unidentified gunmen

Image copyrightAFPImage caption
Checkpoints have been set up in Sloviansk

The attackers, toting assault rifles and wearing camouflage and masks, introduced themselves as fighters of the "people's militia" and addressed residents, the report said.

"We are not Ukrainian troops, we are people's militia. We are the people who have risen up to drive away the corrupt Kiev police," the attackers said.

Video clips running on Ukraine's Hromadske TV appear to show scenes at dusk outside the police building at Kramatorsk, with people gathered on nearby streets watching.

At one point in the unverified video clips, loud and prolonged firing can be heard.

Earlier, the acting Interior Minister, Arsen Avakov, had written on his Facebook page that an attack involving shooting was under way in Kramatorsk.

Trouble continued in several towns and cities on Saturday despite the Kiev government setting a deadline of Friday for all occupations to end. In other incidents:

Gunmen occupied a police station and a security services building in the town of Sloviansk

Official buildings in the town of Druzhkovka were also reported to have been taken over

An attack on police buildings in Krasny Liman late on Saturday was repelled, officials said

A Donetsk regional police chief quit after pro-Russia crowds marched on a police station demanding his resignation.

Protesters in Donetsk city continued to occupy government buildings, demanding a referendum on becoming part of Russia.

'Tough response'

In the attack in the town of Sloviansk, dozens of unidentified armed men in camouflage uniform seized the police station and security service premises.

The aim of the attack at the police station - according to the Interior Ministry - was to seize arms as some 40 automatic rifles and 400 pistols were stored there along with ammunition.

But a member of the group involved in the Sloviansk seizure said they wanted to fight people who represented the "illegal authorities" of interim President Oleksandr Turchynov, according to a video posted on YouTube.

Interviewed in Russian, the man said they represented the People's Front of Donbass - the industrial Donets Basin region in eastern Ukraine.

He said those involved were peaceful Donbass residents and "not fascists".